1. Field of the Invention
The present invention relates to a method for injecting fuel into a multi-cylinder internal combustion engine.
2. Description of the Prior Art
When starting a gasoline engine, it is known to supply each of the cylinders once with what is known as a pilot injection in order to wet the cylinder walls and simultaneously provide an ignitable mixture for the first combustion. Since at this point in time the camshaft and the crankshaft are not yet synchronized and the position of the pistons is unknown, a selective pilot injection strategy is required in order to minimize the emission of non-combusted fuel and hence the pollutant emissions during the start.
In a method known from EP 0 371 158 B1, the cylinders are divided into a first and a second cylinder group according to the two different levels of the camshaft signal. The cylinders of the first group are supplied simultaneously with the pilot injections immediately after a start detection (group injection), while the cylinders of the second group are supplied with the pilot injections with a time delay, and in fact either in a preset sequence or in a normal sequential sequence depending on whether camshaft and crankshaft have already been synchronized.
It has now proved that in this method, in 50% of all starts, not all pilot injections for the cylinders of the first group reach combustion, since some of the pilot injections coincide with an open inlet valve or an inlet valve that is just closing, depending on the stationary position of the internal combustion engine and the position of the inlet valves. Such a situation should be avoided, bearing in mind the increasingly strict statutory regulations on exhaust emissions. An excess fuel emission of this type could be avoided by not releasing the pilot injections until the exact position and relationship between crankshaft and camshaft are known, so that then a “sequential start” might be performed. The result would be a delayed start, however.